.app-header {
  position: sticky;
  top: 0;
  z-index: 50;
  padding-top: env(safe-area-inset-top);
  background: color-mix(in srgb, var(--surface) 92%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.app-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 12px calc(16px + env(safe-area-inset-right)) 8px calc(16px + env(safe-area-inset-left));
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  min-width: 0;
}

.brand__mark {
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  border-radius: 10px;
  background: linear-gradient(145deg, var(--primary), var(--accent));
  color: #fff;
  flex: none;
}

.brand__text {
  display: flex;
  flex-direction: column;
  min-width: 0;
}

.brand__name {
  font-size: 18px;
  font-weight: 750;
  letter-spacing: -0.02em;
}

.brand__tagline {
  font-size: 11.5px;
  color: var(--text-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.app-nav {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 calc(16px + env(safe-area-inset-right)) 0 calc(16px + env(safe-area-inset-left));
}

.nav-list {
  display: flex;
  gap: 4px;
  list-style: none;
  margin: 0;
  padding: 0 0 8px;
  overflow-x: auto;
  overscroll-behavior-x: contain;
  scrollbar-width: none;
  -webkit-overflow-scrolling: touch;
}

.nav-list::-webkit-scrollbar {
  display: none;
}

.nav-link {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  min-height: 44px;
  padding: 8px 13px;
  border-radius: 999px;
  border: 1px solid transparent;
  color: var(--text-muted);
  font-size: 13.5px;
  font-weight: 600;
  text-decoration: none;
  white-space: nowrap;
  transition: background 0.15s ease, color 0.15s ease;
}

.nav-link--active {
  background: var(--primary-soft);
  border-color: color-mix(in srgb, var(--primary) 35%, transparent);
  color: var(--primary);
}

@media (hover: hover) and (pointer: fine) {
  .nav-link:hover {
    background: var(--surface-3);
    color: var(--text);
  }
}

.theme-icon {
  display: grid;
  place-items: center;
}

.app-main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 20px calc(16px + env(safe-area-inset-right)) calc(56px + env(safe-area-inset-bottom)) calc(16px + env(safe-area-inset-left));
}

.app-main:focus {
  outline: none;
}

.app-footer {
  border-top: 1px solid var(--border);
  background: var(--surface);
  padding: 20px calc(16px + env(safe-area-inset-right)) calc(28px + env(safe-area-inset-bottom)) calc(16px + env(safe-area-inset-left));
}

.app-footer__line {
  max-width: var(--max-width);
  margin: 0 auto 6px;
  font-size: 13px;
  font-weight: 650;
  color: var(--text);
}

.app-footer__note {
  max-width: var(--max-width);
  margin: 0 auto;
  font-size: 12px;
  color: var(--text-faint);
  line-height: 1.5;
}

/* ---------- page scaffolding ---------- */
.page {
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.page-head {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.page-title {
  font-size: clamp(20px, 4vw, 26px);
}

.page-sub {
  color: var(--text-muted);
  font-size: 14px;
  max-width: 74ch;
}

.panel {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  box-shadow: var(--shadow-sm);
}

.panel-head {
  margin-bottom: 12px;
}

.panel-title {
  font-size: 15.5px;
  letter-spacing: 0.01em;
}

.panel-sub {
  color: var(--text-muted);
  font-size: 13px;
  margin-top: 3px;
}

.form-card {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  padding: 16px;
  margin: 0 0 14px;
  box-shadow: var(--shadow-sm);
  min-width: 0;
}

.form-card:last-child {
  margin-bottom: 0;
}

.form-card-title {
  padding: 0 6px;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--primary);
}

.toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: flex-end;
  gap: 12px;
  padding: 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
}

.toolbar--filters .field--inline {
  flex: 1 1 180px;
}

.toolbar-actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.field--inline {
  min-width: 150px;
}

.field--grow {
  flex: 2 1 240px;
}

/* ---------- calculator grid ---------- */
.calc-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 18px;
  align-items: start;
}

.calc-col {
  display: flex;
  flex-direction: column;
  gap: 18px;
  min-width: 0;
}

/* ---------- multi grid ---------- */
.multi-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 18px;
  align-items: start;
}

.multi-col {
  display: flex;
  flex-direction: column;
  gap: 18px;
  min-width: 0;
}

/* ---------- settings / guide ---------- */
.settings-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 18px;
}

.settings-data {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.data-stat {
  font-size: 14px;
  font-weight: 600;
}

.form-actions--sticky {
  position: sticky;
  bottom: 0;
  padding: 14px;
  padding-bottom: calc(14px + env(safe-area-inset-bottom));
  margin-top: 0;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-md);
}

.guide-body {
  display: flex;
  flex-direction: column;
  gap: 18px;
  max-width: 900px;
}

.guide-section .panel-title {
  margin-bottom: 10px;
}

.guide-text {
  color: var(--text-muted);
  font-size: 14px;
  margin-bottom: 10px;
}

.guide-list {
  display: flex;
  flex-direction: column;
  gap: 7px;
  color: var(--text-muted);
  font-size: 14px;
  margin-bottom: 10px;
}

.guide-list:last-child {
  margin-bottom: 0;
}

.guide-code {
  margin: 0 0 12px;
  padding: 12px 14px;
  border-radius: var(--radius-sm);
  background: var(--surface-2);
  border: 1px solid var(--border);
  font-family: var(--font-mono);
  font-size: 12.5px;
  line-height: 1.6;
  overflow-x: auto;
  color: var(--text);
}

/* ---------- responsive ---------- */
@media (min-width: 640px) {
  .field-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .field-grid > .field-pair,
  .field-grid > .field-triple,
  .field-grid > .switch-row,
  .field-grid > .radio-group,
  .field-grid > .form-actions,
  .field-grid > .field:has(textarea) {
    grid-column: 1 / -1;
  }
}

@media (min-width: 768px) {
  .settings-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .settings-grid > .panel:has(.form-actions--sticky),
  .settings-grid > .form-actions--sticky {
    grid-column: 1 / -1;
  }
}

@media (min-width: 1024px) {
  body {
    font-size: 15.5px;
  }

  .app-header__inner {
    padding: 14px calc(24px + env(safe-area-inset-right)) 8px calc(24px + env(safe-area-inset-left));
  }

  .app-nav {
    padding: 0 calc(24px + env(safe-area-inset-right)) 0 calc(24px + env(safe-area-inset-left));
  }

  .nav-list {
    overflow: visible;
    justify-content: center;
  }

  .app-main {
    padding: 28px calc(24px + env(safe-area-inset-right)) calc(72px + env(safe-area-inset-bottom)) calc(24px + env(safe-area-inset-left));
  }

  .app-footer {
    padding: 24px calc(24px + env(safe-area-inset-right)) calc(24px + env(safe-area-inset-bottom)) calc(24px + env(safe-area-inset-left));
  }

  .calc-grid {
    grid-template-columns: minmax(0, 1.02fr) minmax(0, 0.98fr);
    gap: 24px;
  }

  .multi-grid {
    grid-template-columns: minmax(0, 1.05fr) minmax(0, 0.95fr);
    gap: 24px;
  }

  .settings-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 400px) {
  .field-pair,
  .field-triple {
    grid-template-columns: minmax(0, 1fr);
  }

  .brand__tagline {
    display: none;
  }
}